1. Field of the Invention
The present invention relates generally to a method for the handover of a mobile terminal and, more particularly, to a handover method that is capable of reducing the handover time and the number of packets that are required to scan channels, and also reducing the amount of traffic that is imposed on a base station by sharing base station information through grouping.
2. Description of the Related Art
With a sharp increase in the use of mobile services, an IEEE 802.11 wireless local area communication network (WLAN) has emerged as an effective alternative to a local area communication network (LAN).
Mobility support in a conventional IEEE 802.11 environment, such as a home or small office network, is not a serious issue because a single access point is often sufficient.
For the quality of service (QoS) demanded by real-time applications such as VoIP and multimedia, however, seamless handover support has become an important requirement for mobility.
802.16e-based wireless networks can be used in various places such as institutions of higher learning, restaurants, and shops. Actually, numerous cities, including San
Francisco, Paris, and Hong Kong, have made plans for deploying such networks that can cover entire city areas. Here, the connectivity is based on self-organizing ad-hoc networks that enable autonomous multi-hop communication between the devices. The devices are able to exchange data even over multiple intermediate devices by handover.
Accordingly, handover is a significant mechanism that is required to fulfill the requirement of constant data transfer when mobile stations (MSs) cross the area overlapped between adjacent base stations (BSs) of wireless networks.
Handover is classified into mobile station (MS) handover and base station (BS) handover according to the device which starts it first. The present invention is intended for MS handover. Handover requires the exchange of data among BSs, which is described in the 802.16e standard.
From among candidate BSs for handover, the most appropriate BS is selected as a target BS. An MS that requires handover sends a message to a serving BS. The message includes the identifier of the target BS.
WiMAX needs to efficiently support the mobility of an MS. Most research into handover aims to reduce delay that occurs during handover.
In related preceding paper 1, Sik Choi, Gyung-Ho Hwang, Taesoo Kwon, Ae-Ri Lim and Dong-Ho Cho, “Fast Handover Scheme for Real-Time Downlink Services in IEEE 802.16e BWA System,” Vehicular Technology Conference, 2005, vol. 3, pp. 2028-2032, the authors suggest a scheme for reducing the time for waiting for down-link packets during a handover process. In this scheme, packets are transmitted between an MS and a BS without verification. In a scheme, an MS forcibly selects a target BS in order to reduce the handover waiting time. Although this scheme can reduce the time it takes to search for a BS and perform synchronization with the BS, it is problematic in that frequent re-scanning resulting from rapid changes in a mobile environment causes time overhead. Furthermore, the probability of handover dropping may increase the time limit.
In related preceding paper 2, Jui-Hung Yeh, Jyh-Cheng Chen, PrathimaAgrawal, “Fast Intra-Network and Cross-Layer Handover (FINCH) for WiMAX and Mobile Internet,” IEEE Transactions on Mobile Computing, April 2009, there is disclosed a scheme that uses active and passive scans at the same time. However, this scheme still requires a lot of active scanning, which is as slow as passive scanning.
Recently, Predictive Channel Reservation (PCR) techniques, for example, a distance and time-based resource reservation technique, were proposed so as to reserve resources. However, these techniques have the problem of increasing the probability of blocking new handover requests and the number of messages required for handover.